A pressurized-water reactor power plant facility includes steam generators each having a housing having a lower end closed by a tube sheet in which an inverted U-shaped tube bundle, made of many tubes, has its inlet and outlet legs mounted. Inlet and outlet manifold chambers are positioned below the tube sheet for the tube bundle's inlet and outlet legs, respectively, and these chambers are connected in circuit with the pressurized-water coolant pipe line connected with the reactor and provided with a pump so that the coolant continuously circulates through all of these parts, the tube bundle forming, of course, a heat-exchanger. There is a constant supply of feed water to the steam generator's housing and the latter has a stream output outlet for the steam produced and which represents useable power from the reactor.
The manifold chambers are ordinarily formed by an inverted hemispherical wall having a dividing partition to form the inlet and outlet manifold chambers. Each chamber is provided with a suitably closed manhole or access opening. After the facility has been in operation for a time, the water coolant circulating through the chambers develops a radiation activity which is transmitted to the inside of the chambers and the tubes of the tube bundle.
When considered necessary, the coolant flow through the steam generator is stopped and via the access openings the heat-exchanger's tubes are internally inspected and possibly repaired, this requiring the insertion of a device in one or more of the tube bundle's tubes. Such a device may comprise a miniaturized camera, a fiber-optics rod, and for repair, an explosively expandable plug for putting a faulty tube safely out of service.
Because of the access opening of such a chamber being offset from alignment with the heat-exchanger tube's ends, the insertion of such a device in any one of the tubes has involved an undesirably prolonged exposure of the workman to the radiation activity existing in the chamber, thus presenting a problem requiring a solution.